The present invention relates to a mechanical fuse for cutting off power transmission when an overload occurs in a power transmission device to protect the safety of the device, and a method of manufacturing the same.
The mechanical fuse is provided, for example, in a power transmission device interposed between a driving side and a driven side (for example, between a driving shaft and a driven shaft) for transmitting the rotating power of the driving side to the driven side. It acts to break down by itself cut off power transmission by force when a large difference occurs between the driving side and the driven side in the midst of transmission of rotating power, thereby avoiding occurrence of lock or rupture due to propagation of overload torque to one side.
Such mechanical fuse is generally composed of a rupture member which is substantially ruptured, disposed between two fixing members fixed to the driving side and driven side so as to link these fixing members. The rupture member is specifically shear pin or shear plate, which is required to be ruptured securely when a specified torque is applied. The magnitude of the torque to lead to rupture can be adjusted by the material and sectional area of the rupture member, but if the rupture member is made of an unstable material which is lowered in strength by fatigue due to repeated exposures to load, the reliability is low and it is not practical. As the material for satisfying such requirements, hitherto, ceramics have been widely used because of stability in fatigue strength and high fatigue limit ratio (ratio of fatigue strength to tensile strength, determined by fatigue strength÷tensile strength).
Ceramics are stable in fatigue strength, but are expensive, and hence inexpensive mechanical fuses have been demanded. There is also a need for mechanical fuse in a form of integrating rupture members to fixing members at both sides and interposing rupture portion between fixing portions for the purpose of improving the assembling efficiency and generality, but the mechanical fuse in this form is not used at the present, because there are problems in that it is hard to assure the strength of fixing portions and in that broken pieces scatter about when it is ruptured.